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This contribution assesses the oxidation of the commonly used insecticide and termiticide, alpha-cypermethrin to polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F, dioxins) and their precursors, under non-catalytic vapour-phase oxidation, in a flow reactor. No soot was produced during the reaction ruling out the de novo synthesis of PCDD/F. The results span the effect of temperature (300-650°C) and fuel equivalence ratio (of 0.01-7.0), at a residence time of 1 s. XAD-2 resin trapped the PCDD/F which were identified and quantitated by high resolution gas chromatography (HRGC)-ion trap mass spectrometry (ITMS). The reactor walls appear to have no noticeable effect on the initiation of the gas-phase oxidation reactions. The decomposition of alpha-cypermethrin produces two types of PCDD/F precursors, chlorinated benzenes (CBz)/chlorinated phenols (CP) and two-ring species, mainly diphenyl ether and chlorinated diphenyl ethers (CDPE). The CBz/CP precursors comprise chlorobenzene, o-, m- and p-dichlorobenzene, 1,2,3-trichlorobenzene, phenol, 2-monochlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-TriCP, with minor amount of 2,4,5-TriCP. The highest emission factor for PCDD/F was observed at 550°C and a fuel equivalence ratio of 0.03, corresponding to 19 ng ∑TEQ-WHO2005/g of alpha-cypermethrin and the total dioxins concentration of 141 μg/g of alpha-cypermethrin. These emissions are one of the highest measured from oxidation of presently used pesticides.

A large number of investigations have been reported on minimising the PAH and PCDD/F yields during controlled combustion, such as incineration. This study is an attempt to quantify acute and chronic toxicants including PAH and PCDD/F in conditions relating to unwanted fires. This paper investigates distribution patterns of fire effluents between gas and aerosol phase, and the different particle size-ranges produced under different fire conditions. PVC carpet was selected as the fuel as a precursor for both PAH and PCDD/F. In order to generate fire effluents under controlled fire conditions, the steady-state tube furnace, was chosen as the physical fire model. Fire scenarios included oxidative pyrolysis, well-ventilated and under-ventilated fires. Fire effluent measurements included: carbon monoxide, carbon dioxide, hydrogen chloride, polycyclic aromatic hydrocarbons, chlorinated dibenzo-dioxins and furans and soot. The distribution patterns between gas and particle phase, and the size-ranges of the particles produced in these fires together with their chemical composition is also reported. Significant quantities of respirable submicron particles were detected, together with a range of PAHs. Lower levels of halogenated dioxins were detected in the fire residue compared with those found in other studies. Nevertheless, the findings do have implications for the health and safety of fire and rescue personnel, fire investigators, and other individuals exposed to the residue from unwanted fires., AuthorCount:7

A large number of investigations have been reported on minimising the PAH and PCDD/F yields during controlled combustion, such as incineration. This study is an attempt to quantify acute and chronic toxicants including PAH and PCDD/F in conditions relating to unwanted fires.This paper investigates distribution patterns of fire effluents between gas and aerosol phase, and the different particle size-ranges produced under different fire conditions. PVC carpet was selected as the fuel as a precursor for both PAH and PCDD/F. In order to generate fire effluents under controlled fire conditions, the steady-state tube furnace, was chosen as the physical fire model. Fire scenarios included oxidative pyrolysis, well-ventilated and under-ventilated fires. Fire effluent measurements included: carbon monoxide, carbon dioxide, hydrogen chloride, polycyclic aromatic hydrocarbons, chlorinated dibenzo-dioxins and furans and soot. The distribution patterns between gas and particle phase, and the size-ranges of the particles produced in these fires together with their chemical composition is also reported.Significant quantities of respirable submicron particles were detected, together with a range of PAHs. Lower levels of halogenated dioxins were detected in the fire residue compared with those found in other studies. Nevertheless, the findings do have implications for the health and safety of fire and rescue personnel, fire investigators, and other individuals exposed to the residue from unwanted fires.

A large number of investigations have been reported on minimising the PAH and PCDD/F yields during controlled combustion, such as incineration. This study is an attempt to quantify acute and chronic toxicants including PAH and PCDD/F in conditions relating to unwanted fires. This paper investigates distribution patterns of fire effluents between gas and aerosol phase, and the different particle size-ranges produced under different fire conditions. PVC carpet was selected as the fuel as a precursor for both PAH and PCDD/F. In order to generate fire effluents under controlled fire conditions, the steady-state tube furnace, was chosen as the physical fire model. Fire scenarios included oxidative pyrolysis, well-ventilated and under-ventilated fires. Fire effluent measurements included: carbon monoxide, carbon dioxide, hydrogen chloride, polycyclic aromatic hydrocarbons, chlorinated dibenzo-dioxins and furans and soot. The distribution patterns between gas and particle phase, and the size-ranges of the particles produced in these fires together with their chemical composition is also reported. Significant quantities of respirable submicron particles were detected, together with a range of PAHs. Lower levels of halogenated dioxins were detected in the fire residue compared with those found in other studies. Nevertheless, the findings do have implications for the health and safety of fire and rescue personnel, fire investigators, and other individuals exposed to the residue from unwanted fires.

Phthalimide (PI) and tetrahydrophthalimide (THPI) are two structurally similar compounds extensively used as intermediates for the synthesis of variety of industrial chemicals. This paper investigates the thermal decomposition of PI and THPI under oxygen rich to oxygen lean conditions, quantifying the production of toxicants and explaining their formation pathways. The experiments involved a plug flow reactor followed by silica cartridges, activated charcoal trap and a condenser, with the decomposition products identified and quantified by Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS) and micro gas chromatography (μGC). The density functional theory (DFT) calculations served to obtain dissociation energies and reaction pathways, to elucidate the reaction mechanism. The oxidation of PI and THPI produced several toxic nitrogen-containing gases and volatile organic compounds, including hydrogen cyanide, isocyanic acid, nitrogen oxides, benzonitrile, maleimide and tentatively identified benzenemethanimine. The detection of dibenzo-P-dioxin (DD) and dibenzofuran (DF) suggests potential formation of the toxic persistent organic pollutants (POPs) in fires involving PI and THPI, in presence of a chlorine source. The oxidation of THPI produced 2-cyclohexen-1-one, a toxic unsaturated ketone. The results of the present study provide the data for quantitative risk assessments of emissions of toxicants in combustion processes involving PI and THPI.

This study assessed the emission of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD and PCDF) from captan, a commonly used fungicide, in vapour-phase oxidative pyrolysis under conditions similar to those encountered in fires and burning biomass contaminated or treated with pesticides. The laboratory-scale apparatus consisted of a pesticide vaporiser, a tubular reactor and a product sampling system. The sampling train comprised tandem XAD-2 resin cartridges to trap PCDD/F as well as an activated charcoal tube to capture the organic volatile compounds (VOC). The analyses of PCDD/F were conducted by means of high resolution gas chromatograph (HRGC) - ion trap mass spectrometer (ITMS) and analyses of VOC by HRGC - quadrupole mass spectrometer (QMS). Substantially more PCDF formed than PCDD in the oxidative pyrolysis of captan, with higher yield of total PCDD/F observed at longer residence time. As indicated by the homologue distribution of PCDD/F, only mono to tetra chlorinated congeners were detected in our measurements, with 4-monochlorinated dibenzofuran (4-MCDF) ranking as the most abundant congener. The results of VOC analysis revealed benzene and chlorinated benzenes as important PCDD/F precursors. Combining the experimental measurements and the results of quantum chemical calculations, we established the reaction pathways for formation of PCDD/F from the vapour-phase oxidative pyrolysis of this widely employed fungicide.

Captan belongs to an important group of sulfenimide fungicides, commonly used on major crops, fruits and ornamentals. In this study, a laboratory scale apparatus has been constructed to investigate the thermal decomposition of captan in gas phase reactions, similar to those that occur in fires, burning of wood and other biomass treated or contaminated with pesticides. The apparatus comprises a plug flow reactor equipped with sampling systems for gaseous, volatile and condensable products. The gaseous species were detected and quantified by the Fourier transform infra-red spectroscopy (FTIR). The volatile organic compounds (VOC) were trapped in an activated charcoal tube and the condensable products were collected by XAD resin and cold solvent traps. The identification of VOC was performed by means of high resolution gas chromatography-quadrupole mass spectrometry (HRGC-QMS). Under oxidative atmosphere, the thermal decomposition of captan generated gaseous pollutants including carbonyl sulfide, carbon disulfide, thiophosgene and phosgene (the World War I chemical agent). The VOC analysis revealed the formation of tetrachlorocthylene, hexachloroenthane (both suspect carcinogens) and chlorinated benzenes. At higher temperature, the decomposition of captan vapour produced, mono to tetra, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), with PCDD/F quantified on an HRGC-MS/MS (ion trap) instrument.